PURPOSE: To provide a converter for controlling the exhaust emission capable of withstanding the use for a long time without erosion of a seal layer by the high temperature exhaust emission.

CONSTITUTION: A plate-shaped ceramic fiber is placed in an airtight sheet 32, and the thickness is reduced by evacuating the inside, and the bulk density of the ceramics fiber is 0.10-0.40g/cm3. The thickness is 1.0-2.5 times the clearance between a catalyst holder 4 and shells 21, 22 after assembly. Then, the air-tight sheet is sealed to make the fiber seal body. The end surface and its periphery of the air-tight sheet are reinforced by wire mesh 5 made of stainless steel, and this reinforced fiber seal body is arranged between the catalyst holder and the shells, and the pressure is applied to be assembled.